The present disclosure is related to the field of radiographic imaging, radiotherapy and analysis thereof. More specifically, the present disclosure is related to phantoms/material, and methods of using these phantoms for radiological purposes.
X-rays and other radiological techniques are important diagnostic and therapeutic tools. However, the measurement of absorbed doses within and around irradiated body tissues necessitates calibration of these radiographic devices with phantoms constructed of carefully selected materials. The use of such phantoms permits determination of absorbed doses when information on the energy and nature of the charged particles at the point of interest is incomplete or fragmentary.
The International Commission on the Radiation Unit and Measurements (ICRU) in its report entitled “Tissue Substitutes in Radiation Dosimetry and Measurement” provides approximate elemental, radiographic, and other physical properties for average body tissues, including brain tissue. The report provides physical quantities for consideration in the selection of tissue substitutes for dosimetric studies and other measurements involving photons, electrons, neutrons, and heavy charged particles. The report further provides the elemental compositions, mass densities, and electron densities of average body tissues. The report also includes recommended elemental compositions in physical characteristics for tissue substitutes. For example, the ICRU Report 44 suggests a brain composition of 10.7% hydrogen, 14.5% carbon, 2.2% nitrogen, 71.2% oxygen, 0.3% chlorine, 0.2% sodium, 0.2% sulfur, 0.4% phosphorus, and 0.3% potassium. The report also notes that the average brain tissue has a physical density of 1.040 g/cm3.
The inventor has recognized that previous attempts at modeling brain tissue for phantoms for use in calibration or dosimetry procedures have typically been accurate at specific imaging energies. However, with the increase in prevalence of low dose radiographic imaging, particularly low-dose CT imaging, and multiple energy CT imaging, a brain tissue phantom that accurately exhibits the radiographic properties of brain tissue over a wide range of X-ray energies is required.
A further challenge to the development of radiographic phantoms of brain tissue is to minimize the inherent compositional differences between actual brain tissue and the brain-equivalent material, yet provide a material that is solid and usable as a phantom at standard temperature and pressure. A typical brain phantom material is constructed of an epoxy, acrylic, or polyethylene base, which is modified by other elements to achieve a desired elemental composition, physical density, effective atomic number, electron density, and radio density such that the attenuating and scattering characteristics closely resemble that of brain tissue.